Scanning apparatus for driving an electrostatic recording structure



Ju|e '30, 1970 c. s. MITCHELL 3,518,699

'f SCANNING APPARATUS FOR DRIVING AN ELECTROSTATIC REcoRnme'sTnucTuREFiled on 25.1967

PRINT COMMAND CONTROL CIRCUIT CAM DRIVER come & rmmc cmcun INVENTORCHARLES S. MITCHELL ATTORNEY United States Patent 3,518,699 SCANNINGAPPARATUS FOR DRIVING AN ELEC- TROSTATIC RECORDING STRUCTURE Charles S.Mitchell, Palo Alto, Calif., assignor to Hewlett- Packard Company, PaloAlto, Calif., a corporation of California Filed Oct. 23, 1967, Ser. No.677,316 Int. Cl. G01d 15/06; H04n N16 US. Cl. 346-74 14 Claims ABSTRACTOF THE DISCLOSURE A cam follower is supported for being driven back andforth across an electrosensitive recording sheet as it follows arotatable helical cam. An electrode structure is coupled to the camfollower for selectively discharging current into the recording sheet toprint a line of alphanumeric characters thereon as the follower isdriven across the recording sheet in one direction from an idleposition. The cam follower helps to turn the electrodes into an anoperative position when recording is to occur. The recording sheet isadvanced to the position of a new line as the following is driven acrossthe recording sheet in the opposite direction back to the idle position.

SUMMARY OF THE INVENTION According to the illustrated embodiment of thisinvention, record forming means is driven back andforth across arecording medium by a cam follower that is supported for reciprocatinglinear motion across the recording medium while following a rotatablehelical cam. The follower is shaped like an inverted T, the cross bar ofwhich "follows the helical cam and the leg of which is coupled to therecord forming means so that the angle of the helical cam controls theposition and velocity of the record forming means as the record formingmeans is driven across the recording medium. The angle of the helicalcam positions the record forming means in contact with the recordingmedium as the record forming means is driven across the recording mediumin one direction froman idle position to print a line. Similarly, theangle of the helical cam positions the record forming means away fromthe recording medium as the record forming means is driven across therecording medium in the opposite direction hack to the idle position. Atwisted flat member is coupledto a capstan and to the cam follower fordriving the capstan to advance the recording medium to the position of anew line only during the return of the follower and record forming meansto the idle position. Apparatus is also provided for smoothly startingthe follower along the helical cam from the idle position in which thefollower is disengaged from the helical cam.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now the drawing, whichis a perspective view of the preferred embodiment of the invention,there is shown a recording medium in the form of a sheet ofelectrosensitive recording paper which produces a contrasting mark whenelectric current is passed through it. An example of suchelectrosensitive recording paper is described in the copending patentapplication Ser. No. 358,191 filed by Charles S. 'Reis on Apr. 8, 1964,issued as US. Pat. No. 3,411,948 on Nov. 19, 1968, and entitledElectrosensitive Recording Medium. A line of alphanumeric characters 12may be printed on the electrosensitive sheet 10 with a record formingmeans comprising, for example, a vertical row of seven electrodes 14insulated and equidistantly spaced from each other. Each alphanumericcharacter is printed by linearly moving the row of electrodes 14 acrossthe sheet 10 and by applying electrical impulses to selected electrodes14 at one to five successive positions of the row of electrodes as itmoves across the sheet. Each electrode 14 to which an electrical impulseis applied at one of these positions discharges through the electricallyconductive sheet '10 to a stationary electrode 16. This forms on sheet10 a pattern of discrete dots defining the alphanumeric character. Acoding and timing circuit 11 responsive, for example, to the output of adesk calculator may be employed for supplying coded electrical impulsesin the appropriate time sequence to the electrodes '14 as required toproduce each alphanumeric character.

The electrodes 14 may be poles of a high temperature alloy such astungsten formed at the end of signal carrying wires. They must withstandthe intense heat resulting from rapid electrical discharge. Thestationary electrode 16, if disposed on the same side of sheet 10 aselectrodes 14, may serve to hold sheet 10 down against a capstan 18 thatdrives the sheet forward to expose a clean area so a new line can beprinted.

The electrodes I14 are moved in parallel straight lines and at aconstant linear velocity across sheet 10 by follower means that issupported for reciprocating linear motion across the sheet whilefollowing a helical cam groove 24 on the surface of a rotatablecylindrical element 22 that is driven by a cam driver 9 such as a motor.This follower means comprises a cam follower element 26 and a followercarriage 20 for restraining the cam follower element 26 to linear motionacross sheet 10 along a path defined by constraining guide bars 21. Theangular velocity of cylindrical element 22 and the angle of helical camgroove 24 with respect to the axis of cylindrical element 22 control thelinear velocity of cam follower element 26 and electrodes '14 acrosssheet 10. If these parameters are constant, the velocity of electrodes14 will be constant across sheet 10. Essentially, the velocity of camfollower element 26 is directly proportional to the helix angle *for agiven cam rotational velocity. Helical cam groove 24 runs alongcylindrical element 22 from a rest or idle position near one end of thecylindrical element to a position near the other end of the cylindricalelement, as specifically indicated by the reference numeral 24a. It thenruns back along cylindrical element 22 to the rest or idle position, asspecifically indicated by the reference numeral 24b. The rest or idleposition is defined by a groove 23 running circumferentially aroundcylindrical element 22. This groove 23 comprises a substantiallyzero-rise cam allowing cylindrical element 22 to turn without anyresulting linear motion of cam follower element 26.

Cam follower element 26 is shaped like an inverted T, the leg of whichpasses freely through a bearing in the main body of follower carriage20. Cam follower element 26 is thus free to rotate on the axis of itsleg as its cross bar follows the angle of the helical cam groove 24.Electrodes 14 are rigidly attached to the leg or cam follower element 26so that they are positioned in a non-printing position away from thesheet 10 when the cam follower element is in the idle position. Theturning of cam follower element 26 as it enters helical cam groove 24afrom the idle position in circumferential groove 23 moves electrodes 14into a printing position in contact with sheet 10 as shown in the brokenline representation of electrodes 14. Similarly, the turning of camfollower element 26 as it begins the return path along helical camgroove 24b back to the idle position in circumferential groove 23 againmoves electrodes 14 to a non-printing position away from sheet .10. Thecross bar of the T-shaped cam follower element 26 also serves toproperly guide the cam follower element along cam groove 24 even thoughgroove portions 24a and 24b cross one another.

Cam follower element 26 rides in the idle position in circumferentialgroove 23 until a print command control circuit 25 actuates a solenoid28 to push the leading end of the cross bar of cam follower element 26into helical groove 24a. Interlock detecting means 30 is used to detectthe position of cylindrical element 22 at which solenoid 28 must beactuated to insure that cam follower element 26 smoothly enters camgroove 24a. This interlock detecting means 30 may comprise a mechanicalmicroswitch or an encoder for detecting the instantaneous position ofcylindrical element 22. The interlock detecting means 30 is connected tothe print command control circuit 25 for inhibiting actuation ofsolenoid 28 until detection of the position of cylindrical element 22 atwhich cam follower element 26 may be smoothly inserted into cam groove24a. Once the cross bar of cam follower element 26 enters cam groove24a, the electrodes 14 attached to the leg of cam follower element 26are driven in the printing position and at a constant linear velocityacross sheet by rotation of cylindrical element 22 at a constant angularvelocity. As electrodes 14 are driven across sheet 10 in the printingposition, they are selectively supplied with electrical impulses as fromthe coding and timing circuit 11 to print a line of alphanumericcharacters. At the end of this printing scan the angle of cam groove 24adiminishes to zero thereby moving electrodes 14 away from sheet 10 andmomentarily bringing cam follower element 26 to a stop. The angle of camgroove 24b then builds up in the opposite direction so that electrodes14 are moved still further away from the paper and returned with camfollower element 26 to the idle position in circumferential groove 23.Cam follower element 26 remains in this idle position with attachedelectrodes 14 in a non-printing position away from sheet 10 until aprint command is again initiated as by print command control circuit 25.

Sheet 10 is advanced by capstan .18 during the return of the followermeans to the idle position after a line has been electrically printed onthe sheet. This is accomplished by a twisted flat finger 34 (in effect,a simplified screw gear) that runs at one end in a slot 36 in thefollower carriage and that is mechanically coupled at the other end to agear 38. As the follower means scans back and forth across sheet 10, thefollower carriage 20 causes twisted finger 34 to oscillate through anangle determined by the amount of twist in finger 34. The gear 38 mesheswith another gear 40 fixedly attached to one end of the capstan 18 anddrives the capstan to advance sheet 10. Gear 38 is a one Way oroverrunning clutch gear that idles when finger 34 is rotated in theclockwise direction by follower carriage 20 during the printing of aline. It turns and thereby drives capstan 18 to advance sheet 10 onlywhen finger 34 is rotated in the counterclockwise direction by followercarriage 20 as cam follower element 26 returns to the idle positionalong cam groove 24b. The angle of twist of finger 34 and the gear ratiobetween gears 38 and 40 control the amount of sheet advance accomplishedduring each return of the follower means to the idle position and aretherefore selected to provide the desired line spacing on sheet 10.

The capstan 18, the gears 38 and 40, the twisted finger 34, and thestationary electrode 16 may be rigidly coupled together for smalltranslational displacements relative to the electrodes 14 as indicatedby arrows 50. This permits adjustment of the pressure with whichelectrodes 14 bear against sheet 10 and thereby enables the operator toincrease the useful lifetime of electrodes .14.

What is claimed is:

1. Apparatus for scanning a recording medium, said apparatus comprising:

a rotatable element having a helical cam on its surface;

follower means supported for engaging and following said helical cam andfor reciprocally moving across the recording medium While following thehelical cam; and

scanning means coupled to said follower means for reciprocally movingtherewith across the recording medium;

said follower means including means driven by said helical cam forturning said scanning means to an operative position relative to therecording medium during movement of the follower means in one directionacross the recording medium and to an inoperative position relative tothe recording medium during movement of the follower means in theopposite direction across the recording medium.

2. Apparatus as in claim 1 including drive means for moving therecording medium in a predetermined direction, said drive meanscomprising a capstan intermittently driven during movement of saidfollower means in said opposite direction across the recording medium.

3. Apparatus as in claim 2 wherein:

said drive means for moving the recording medium further comprises ascrew gear coupled to said capstan for rotating it in one direction; and

said follower means is movably supported and restrained to linear motionin a direction generally transverse to the direction of movement of saidrecording medium and is coupled to said screw gear for converting thelinear motion of said follower means to rotary motion of said screw gearto drive said capstan.

4. Apparatus as in claim 3 wherein said drive means for moving therecording medium still further comprises a one-way clutch means coupledbetween said screw gear and said capstan for rotating said capstan inonly one direction.

5. Apparatus as in claim 1 including:

idler means for disengaging said follower means from said helical camand for retaining said follower means and said scanning means in an idleposition to prevent them from moving across the recording medium; and

control means for selectively engaging said follower means with saidhelical cam from the idle position whereupon rotation of the rotatableelement reciprocally moves said follower means and said scanning meansacross the recording medium and back to the idle position.

6. Apparatus as in claim 5 wherein:

said scanning means comprises record forming means for producing arecord on the recording medium; and

said control means comprises an electrical solenoid for engaging saidfollower means with said helical cam.

7. Apparatus as in claim 6 wherein said control means further comprises:

a detector means for determining a position of said rotatable elementfor which said follower means may be smoothly engaged with said helicalearn from the idle position; and

means for selectively energizing said electrical solenoid at theposition determined by said detector means.

8. Apparatus as in claim 7 wherein said idler means for retaining saidfollower means in the idle position comprises a substantially zero-risecam on the surface of said rotatable element.

9. Apparatus as in claim 5 wherein:

said helical cam comprises a helical groove in the surface of saidrotatable element;

said follower means is disposed for riding in said helical groove andfor turning with changes in the angle of said groove; and

said scanning means comprises record forming means for producing arecord on the recording medium, said record forming means being moved tothe op erative position relative to the recording medium in response tomovement of said follower means from the idle position along saidhelical groove. 10. Apparatus as in claim 9 wherein said follower meansincludes an inverted generally T-shaped element supported with itscrossbar riding in said helical groove.

11. Apparatus as in claim 10 wherein: said record forming meanscomprises a first electrode structure driven by said follower means andadapted to scan back and forth across the recording medium with saidfollower means in a direction transverse to the direction of movement ofthe recording medium, said first electrode structure including aplurality of conductive electrodes aligned transversely with respect tothe direction of movement of said first electrode structure, saidelectrodes following substantially parallel linear paths as said firstelectrode structure scans across the recording medium; said apparatusincludes a second electrode structure positioned along the recordingmedium; and said apparatus includes circuit means for selectivelyapplying electrical signals to selected ones of the electrodes of saidfirst electrode structure to produce selected patterns of marks on therecording medium one after the other as said first electrode structurescans in said one direction across the recording medium. 12. Apparatusas in claim 11 wherein: said control means for selectively engaging saidfollower means with said helical groove comprises an electricalsolenoid, detector means for determining a position of said rotatableelement for which said follower means may be smoothly engaged with saidhelical groove from the idle position, and means for selectivelyenergizing said electrical solenoid at the position determined by saiddetector means; said idler means for retaining said follower means inthe idle position comprises a substantially zero-like cam on the surfaceof said rotatable element; and

said apparatus includes drive means for moving the recording medium in apredetermined direction, said drive means comprising a capstanintermittently driven during movement of said follower means in saidopposite direction across the recording medium and comprising a screwgear coupled to said capstan by a one-way coupling means for rotatingsaid capstan in one direction;

said follower means is movably supported and restrained to linear motionin a direction generally transverse to the direction of movement of saidrecording medium and has an opening for receiving said screw gear toconvert the linear motion of said follower means to rotary motion ofsaid screw gear to drive said capstan.

13. Apparatus as in claim 12 wherein said first electrode structure andsaid capstan are mounted for relative movement to adjust the pressurewith which the electrodes of said first electrode structure bear againstthe recording medium.

.14. Apparatus as in claim 12 including means for controlling thepressure with which said first electrode structure bears against therecording medium.

References Cited UNITED STATES PATENTS 2/1952 Grib 346139 1/1967Yazejian et al. 346--74 US. Cl. X.R. 1786.6; 346-139 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated June 30, 1970 CS Mitchell Inventor-(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

SIGNED AND SEALED Attest:

M H. Hal-3h. In I. m Amazing Officer Oomiaaiom of Patents Column 1, line23, "following" should read follower Column 6, line 1, "zero-like"should read zero-rise FORM Po-IOSO (IO-69) USCOMM-DC 60376-P5Q Q u sGOVIHNMINY PRINTING OIHEE In, 0-!00-134 -I6OOIO

